New air-pollution limits for diesel engines have caused some manufacturers to adopt selective catalytic reduction (SCR) technology for reducing pollutants, such as nitrogen oxides (NOx), in engine exhaust. The SCR process introduces an NOx reductant, such as urea, into the exhaust stream from a diesel engine. With the help of a solid-phase catalyst, the NOx reductant chemically reduces NOx within the exhaust into non-pollutant compounds.
Diesel exhaust fluid (DEF) is a term used to describe a standardized solution of an NOx reductant. DEF typically comprises a 32.5% (by weight) solution of high-purity urea in demineralized water.
Present governmental regulations allow for DEF to be manually added to a reservoir in the SCR system (e.g., the DEF reservoir can be refilled frequently, similar to a fuel tank). However, operator refilling of DEF is costly and inconvenient, particularly because not all diesel filling stations have a DEF pump. Accordingly, it is desired to develop a technology that facilitates the refilling of a vehicle DEF supply at normal emission-maintenance intervals (e.g., every 150,000 miles) such that professional technicians are primarily responsible for refilling a DEF supply.